Guess it's back to... "Sub Theory Class" 101 - diyAudio
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Old 16th September 2013, 12:40 AM   #1
rigtec is offline rigtec  United States
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Default Guess it's back to... "Sub Theory Class" 101

Hi everyone,

I have a question. I wanted to exploit the full low frequency potential of my suv's recently upgraded (4) ten, 3.2 cuft'(n) sealed sub-woofer enclosure. I just happen to have an empty, 5.1 cuft', 4x10 "Pro-audio" box in storage that I could use in place of that one, provided, it would be beneficial to make the swap. Now in my mind, there are no "free lunches"... so if I increase the size of the box by a HUGE denomination, like 75 to 100%, I'd expect to see some nominal gains in LF "extension" however, some "losses" are to be expected in efficiency, and possibly "power handling"(mech lim). Otoh... If I were to "truncate" an enclosure (by those same denominations), I'd be looking for marginal increases in sensitivity, and power handling (mech lim), but still, some degree of loss in "low frequency extension". Here's where I may be finding some trouble with my hard-core theoretical approach.

I've been running a few sims on winISD. The sub-woofer system consists of: (1) 3.2 cuft'(n) sealed box w/ four, JL Audio 10W6v2-D4, ten inch drivers. The box is "partitioned" down the center; (2) ten's on one side, (2) ten's on the other. The four drivers are fed by two, JL audio (HD-series) 750W Rms, class-D power amps. First, I modeled the four, ten inch JL drivers in a 3.2 cuft' sealed box, and noted the f3 position in the "gain" plot window. Then, I modeled the same four drivers, but in a 5.1 cuft' sealed enclosure but the f3 (43.3), never changed; only the gain "curve radius" (db/octv slpe) became longer, smoother. Just out of curiosity, I placed the drivers in a ten cuft' box, and my f3 remained stable (43.3). So, just for Sh--'s & G's, I put them on a "massive", 200 cuft' I.B. manifold and my f3 begun to ascend (>>46.2); but perhaps that's because the Qts is too low (.5) for that; really thought that I could drive the f3 downward (twd's the "free air res. freq") using a larger box.

"Here's the driver T/S- as published on the mfr's website":

10W6v2-D4: 10-inch (250 mm) Subwoofer Driver, Dual 4 Ω

Free Air Resonance (Fs) 28.5 Hz
Electrical “Q” (Qes) 0.497
Mechanical “Q” (Qms) 8.458
Total Speaker “Q” (Qts) 0.469
Equivalent Compliance (Vas) 1.18 cu ft / 33.4 L
One-Way Linear Excursion (Xmax)* 0.60 in / 15 mm
Reference Efficiency (no) 0.15%
Efficiency (1 W / 1 m)** 83.7 dB SPL
Effective Piston Area (Sd) 51.4 sq in / 0.0332 sq m
DC Resistance (Re)*** 6.3 Ω
* Xmax specifications are derived via one-way voice coil overhang method with no correction factors applied.
*** Re (DC resistance) is measured with the voice coils in series, for parallel-wired specification divide Re by 4. All other specifications remain the same.

"Any theory as to why the f3 never dropped beyond 43.3hz no matter how much area was provided in the box; I know there are other parameters (besides the vas/fb/fs/fc) that factor 'collectively' into these results at some point"?!

rigtec, cheers

Last edited by rigtec; 16th September 2013 at 05:30 PM.
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Old 17th September 2013, 08:15 PM   #2
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Yes, you are right rigtec.
F3 it's insignificant.
As you can see here (site in French, look at the graphics only), that's a common mistake for many diy newbies, as you give more extension (LF) your F3 goes up (lower Qt).
speaker basics
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Old 17th September 2013, 11:15 PM   #3
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In a car, more drivers (or larger drivers and high xmax) and more power in a sealed cabinet, as opposed to a larger more efficient cabinet design.

Btw I don't really see why you'd want more than those (4) 10's plus a clean 1500w rms could provide. Unless this is a db drag race vehicle?

Last edited by m R g S r; 17th September 2013 at 11:44 PM.
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Old 18th September 2013, 01:28 AM   #4
rigtec is offline rigtec  United States
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Quote:
Originally Posted by m R g S r View Post

Btw I don't really see why you'd want more than those (4) 10's plus a clean 1500w rms could provide. Unless this is a db drag race vehicle?
Hahaha! It's not really that I want or need more output; tis' a hobby, a pass time, a therapeutic path(ology) to stay ahead of the things I must do; like work, pay rent, med bills...(etc)! I really enjoy learning this stuff, been doing it since I started playing bass guitar, since 1971. But I've been applying it and studying (pro-audio) since, maybe... '04.

In this case with the truck, I'm merely trying to maximize/explore the full potential of the 'four ten' sealed box; I have so much to learn though, so I'm always trying to create some sort of project with my equipment. PS: Trying not to run out of things to do is the hardest part! Thanks so much for your reply.

Best, rigtec
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Old 18th September 2013, 01:35 AM   #5
Einric is offline Einric  United States
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Does any of your gear allow you to boost around 30hz?
If so I would give a bit of boost to stretch your F3 out.
I had 2 sealed Diamond Audio 10's sealed .75cuft per w/ 1000W and with a bit of boost they were QUITE impressive.
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Old 18th September 2013, 01:41 AM   #6
Einric is offline Einric  United States
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I started w/ 1cuft per woofer and when I pushed them hard I could swear I heard the woofers bottom out.
A local subwoofer guru told me to eat up at least .25 cuff per driver and it would solve the problem.
After I sprayed a bunch of spray foam inside each box the bass got punchier and ALOT more defined.
Then I added a bit of boost around 30hz and never felt the need to touch it again.
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Old 18th September 2013, 01:42 AM   #7
rigtec is offline rigtec  United States
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Quote:
Originally Posted by Inductor View Post
Yes, you are right rigtec.
F3 it's insignificant.
As you can see here (site in French, look at the graphics only), that's a common mistake for many diy newbies, as you give more extension (LF) your F3 goes up (lower Qt).
speaker basics
Hi Inductor,

I'm not quite sure I understand what drives the f3 upwards, in the case of having less pressure (unloaded) on the drivers cone, as in "using a much larger box"; i.e., an "attic manifold" infinite baffle/open baffle (free air) bare with me here...
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Old 18th September 2013, 01:56 AM   #8
rigtec is offline rigtec  United States
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Quote:
Originally Posted by Einric View Post
I started w/ 1cuft per woofer and when I pushed them hard I could swear I heard the woofers bottom out.
A local subwoofer guru told me to eat up at least .25 cuff per driver and it would solve the problem.
After I sprayed a bunch of spray foam inside each box the bass got punchier and ALOT more defined.
Then I added a bit of boost around 30hz and never felt the need to touch it again.
Ok Einric,

The jl (10w6) sub requires 0.625 cuft' per driver. I gave them .8 cuft' each, or 3.2 cuft'(n) divided by 4. The box is stuffed with pollyfill, apprx 1.5 lbs/ ft3. Are you saying that, perhaps, less area in the box translates to better bass?
Thanks for your reply.

rigtec
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Old 18th September 2013, 02:02 AM   #9
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The specs that JL gives for the boxes work well...when used in conjunction with cabin gain.
People say that the box specs they give are grossly undersized. That is true when used in a larger listening environment.
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Old 18th September 2013, 02:08 AM   #10
rigtec is offline rigtec  United States
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Quote:
Originally Posted by Einric View Post
Does any of your gear allow you to boost around 30hz?
If so I would give a bit of boost to stretch your F3 out.
I had 2 sealed Diamond Audio 10's sealed .75cuft per w/ 1000W and with a bit of boost they were QUITE impressive.
No, I don't have any boost on the sub, and the bass is cut @neg 6db at the HU; this sub is an absolute monster, and doesn't need it. However..., I still want to find a parametric eq or graphic eq to do just that, boost at a specific frequency like 25-30hz (just-4-fun)
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